#!/usr/bin/env python3
# Copyright 2019 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""CLI tool that returns URL of the proxy for particular zone and version."""
import argparse
import functools
import json
import logging
import re
import requests

try:
  unicode
except NameError:
  unicode = str

def urls_for_zone(zone, location_to_urls_map):
  """Returns list of potential proxy URLs for a given zone.

  Returns:
    List of possible URLs, in order of proximity.
  Args:
    zone: GCP zone
    location_to_urls_map: Maps region/country/continent to list of URLs, e.g.:
      {
        "us-west1" : [ us-west1-url ],
        "us-east1" : [ us-east1-url ],
        "us" : [ us-west1-url ],
        ...
      }
  """
  zone_match = re.match("((([a-z]+)-[a-z]+)\d+)-[a-z]", zone)
  if not zone_match:
    raise ValueError("Incorrect zone specified: {}".format(zone))

  # e.g. zone = us-west1-b
  region = zone_match.group(1)         # us-west1
  approx_region = zone_match.group(2)  # us-west
  country = zone_match.group(3)        # us

  urls = []
  if region in location_to_urls_map:
    urls.extend(location_to_urls_map[region])

  region_regex = re.compile("([a-z]+-[a-z]+)\d+")
  for location in location_to_urls_map:
    region_match = region_regex.match(location)
    if region_match and region_match.group(1) == approx_region:
      urls.extend(location_to_urls_map[location])

  if country in location_to_urls_map:
    urls.extend(location_to_urls_map[country])

  return set(urls)


def main():
  unicode_type = functools.partial(unicode, encoding="utf8")
  parser = argparse.ArgumentParser(
      description="Get proxy URL")
  parser.add_argument("--config-file-path", required=True, type=unicode_type)
  parser.add_argument("--location", required=True, type=unicode_type)
  parser.add_argument("--version", required=True, type=unicode_type)

  args = parser.parse_args()
  with open(args.config_file_path, "r") as config_file:
    data = json.loads(config_file.read())

  agent_containers_config = data["agent-docker-containers"]
  version = args.version
  if version not in agent_containers_config:
    version = "latest"
  if version not in agent_containers_config:
    raise ValueError("Version latest not found in the config file.")
  container_config = agent_containers_config[version]
  regional_urls = container_config["proxy-urls"]

  location = args.location
  urls = urls_for_zone(location, regional_urls)
  if not urls:
    raise ValueError("No valid URLs found for zone: {}".format(location))

  for url in urls:
    try:
      status_code = requests.head(url).status_code
    except requests.ConnectionError:
      pass
    expected_codes = frozenset([307])
    # 307 - Temporary Redirect, Proxy server sends this if VM has access rights.
    if status_code in expected_codes:
      logging.debug("Status code from the url %s", status_code)
      print(url)
      exit(0)
    logging.debug("Incorrect status_code from the server: %s. Expected: %s",
                  status_code, expected_codes)
  raise ValueError("No working URL found")

if __name__ == '__main__':
  main()